The manufacture of 2,2-bis(4-hydroxyphenyl) propane, or "bisphenol-A" ("BPA") by the reaction of phenol and acetone is well known and practiced commercially. See U.S. Pat. No. 3,242,219 and French Patents 1,179,377, 1,342,760, and 1,353,609.
Commonly produced in such manufacture is a waste stream which may comprise at least 50%, and up to about 90% (by weight) BPA. Because of the difficulty heretofore of recovering the BPA from the waste stream, it is generally burned along with the waste or otherwise disposed of at minimal value. In an HCl-catalyzed process, this stream typically is 3-4% of total plant production. Such waste streams may be produced, for example, in the crystallization processes described in "Industrial Crystallization for Ultrapure Products" by Charles G. Moyers, Jr., CEP May 1986, pp 42-46, and in U.S. Pat. No. 4,209,646.
We are not aware of a process similar to ours which is designed to recover values from a BPA waste stream such as we obtain in our plant, i.e. having from 50-90% para-para BPA (p,p-BPA), 5-35% ortho-para BPA (o,p-BPA) and 0-15% phenol, along with 5 to 30% other, higher molecular weight materials including about 3 to about 15% (based on the whole composition) of a reaction product of phenol and mesityl oxide, 2,2,4-trimethyl-4-hydroxyphenyl-chroman, which will be referred to herein as "codimer" (see the structural formula I below). Such a waste stream may be assumed to be present in the bottoms of column 13, described in the aforementioned U.S. Pat. No. 4,209,646, which is incorporated herein by reference in its entirety.
Additional compounds, included in "other" above, are 2,4,4-trimethyl-2-hydroxyphenyl-chroman (II), the isopropenyl dimer (III), "bisphenol-X", or trisphenol (IV), a spiro compound (V), a compound which may be referred to as "4 ring A" (VI) and one referred to as "14 ring B" (VII). Chroman is a particularly troublesome impurity because its boiling point is slightly lower than p,p-BPA, but higher than o,p-BPA. U.S. Pat. No. 4,954,661 teaches some steps similar to the present invention, but it is more complex and does not address the important issue of codimer removal. ##STR1##